Generally, a surface mounting technology (SMT) for assembling surface mounting devices (SMD) on a printed circuit board (PCB) etc. comprises a technology of miniaturizing and integrating the surface mounting devices, and technologies of developing precise assembly equipment for assembling the surface mounting devices precisely and operating various kinds of assembly equipments.
In this connection, a surface mounting assembly line is consisted of apparatuses such as a surface mounting machine and a vision inspection apparatus, wherein the surface mounting machine, for mounting the surface mounting devices on the printed circuit board, is supplied various kinds of the surface mounting devices supplied in forms such as tape, stick and tray from a feeder and transfers to a mounting position on the printed circuit board, then, locates the devices on a predeterminate position on the printed circuit board, and the vision inspection apparatus inspects whether mounted states for the devices are good or bad before and after the completion of soldering process of the devices, and transfers the printed circuit board to the next process depending upon results obtained through the vision inspection apparatus.
At this time, a vision inspection method using a conventional vision inspection apparatus adjusts an initial position at a position adjusting apparatus when the printed circuit board that the soldering process is completed is transferred through a conveyor, and inspects whether the mounted states are good or bad by photographing soldering positions of various kinds of devices with a camera and outputting illuminating states of the soldering positions at the vision inspection apparatus to a monitor and calculating them when a lighting is illuminated on the printed circuit board after the completion of the adjustment.
However, the prior art vision inspection apparatus and method have problems that each component accompanies large loads on its driving and serious vibrations on its halt since the camera is fixed and the printed circuit board is moved, or the printed circuit board is fixed and the camera is moved for photographing various soldering parts on the printed circuit board, thereby separating the devices from the original position by a vibration of the inspection apparatus itself when the mounted state of the devices is inspected before the soldering process. Further, a wide installation space is required due to a large-scale of the apparatus itself since a movable space of the camera and the printed circuit board should be occupied. In addition, the prior art has a problem that an inspection position cannot visually confirmed during the test since a distance between the camera and an inspection object is close.
On the other hand, Korean Registered Patent No. 340012 has proposed “Object inspection method and computer vision system using a movable mirror”.
FIG. 1 is an overall structural view for illustrating the prior registered invention, and FIG. 2 is a structural view for illustrating an operating state of the prior registered invention.
Referring to FIG. 1, X-Y axis movable mirrors 400 and 500 driven by a high-speed motor, a half mirror 600, and a light source 700 are installed between an inspection area 300 and a camera 200. Therefore, the vision system captures images about small areas in the inspection area 300 and operates the movable mirrors 400 and 500 with a high speed to obtain an image of the entire area, thereby accomplishing an inspection. The vision system 100 of the prior registered invention makes a mechanical movable portion extremely small to increase an inspection speed and vary a light path by using the movable mirror, thereby excluding a mechanical mechanism and minimizing an occurring of noises and shocks.
However, the above-mentioned prior registered invention has a problem as follows.
First, since a distance between the inspection area 300 and the light source 700 is distant, losses of a quantity of light transmitted from the light source 700 to the inspection area 300 and a quantity of light transmitted from the inspection area 300 to the camera 200 become lager in proportion to a square of the distance between the inspection area 300 and the light source 700. That is, brightness of the images transmitted to the camera 200 decreases in inverse proportion to a square of the distance. Especially, the half mirror 600 installed on a light path in order to coincide an image path with an illumination path can not accomplish a precise inspection since the image of the inspection area 300 can not be transmitted clearly to the camera 200 as a quantity of light of the illumination or the image passed through due to its characteristics is lost about a half.
Second, as shown in FIG. 2, light finally illuminated to the inspection area 300 becomes inclined light rather than vertical light as a method of changing a path of light by using the X-Y axis movable mirrors 400 and 500 is employed. While the inclined light has no problem when an object in the inspection area 300 is formed in a plane, when the printed circuit board on which various components having different heights are mounted is inspected, reliability of the inspection is reduced since a clear image can not be obtained due to shadows generated by the each component.